This invention relates to television tuning systems and more particularly to a system for controlling the band of radio frequencies being received to provide for a sequential sweep of a tuner through a plurality of bands.
A tuning system which provides for the selection of any one of a plurality of television channels in, for example three bands of radio frequencies, is disclosed in my copending application Ser. No 476,081 filed concurrently herewith and entitled, "Randon Channel Address Crystal-Lock Tuning System", now U.S. Pat. No. 3,924,192. To access a given channel, data representative to the channel selected is inserted into a memory. An oscillator of an appropriate tuner for tuning one of the three radio frequency bands is swept throughout a band of ocsillator frequencies. As the oscillator is swept, the oscillator signal is compared to a plurality of harmonically related frequency samples which are spaced apart by a frequency related to a regular channel spacing. A counter accumulates a count representative of the number of frequency comparison conditions encountered during a period of sweeping of the oscillator. When the count inserted in the memory equals the count in the counter, sweeping of the oscillator is stopped and the oscillator is held at a frequency determined by one of the harmonically related samples nearest the oscillator frequency and an automatic fine tuning correction signal.
The oscillator of the tuner utilized to tune the first band is modified to tune the second of the three radio frequency bands, and, in the case of the channel allocations employed in the Unites States, a second tuner is activated to tune the third of the three radio frequency bands. The tuning system, therefore, provides a modification of the oscillator to facilitate sweeping more than one band of frequencies or switching to a separator tuner. Also, resetting of the sweep generator upon accumulation of predetermined counts in the counter in the absence of a hold signal is provided.